Venango County was created on March 12, 1800 from parts of Allegheny and Lycoming Counties. The name "Venango" comes from the Native American name of the region, Onenge, meaning Otter. This was corrupted in English as the Venango River.[4] The settlement at its mouth was likewise called Venango, and is the site of present-day South Side of Oil City, Pennsylvania.

Venango County was home to an oil boom in the years following discovery of natural oil (petroleum) in the mid-1850s.

George Bissell, a Yale University Chemistry professor, and Edwin L. Drake, a former railroad conductor, made the first successful use of a drilling rig on August 28, 1859 near Titusville, Pennsylvania. (Although Titusville is in Crawford County, the first oil well was drilled outside of town, less than a mile inside of the Venango County boundary.) This single well soon exceeded the entire cumulative oil output of Europe since the 1650s. Within weeks oil derricks were erected all over the area. Other oil boom towns located in Venango County included Franklin, Oil City, and the now defunct Pithole City The principal product of the oil was kerosene.

After joining Standard Oil, Rogers invested heavily in various industries, including copper, steel, mining, and railways. The Virginian Railway is widely considered his final life's achievement. Rogers amassed a great fortune, estimated at over $100 million, and became one of the wealthiest men in the United States. He was also a generous philanthropist, providing many public works for his hometown of Fairhaven, Massachusetts, and financially assisting helping such notables as Mark Twain, Helen Keller, and Dr. Booker T. Washington.

Perhaps in one of history's ironies, another resident of Venango County about the same time as Henry and Abbie Rogers was a little girl named Ida M. Tarbell, whose father was an independent producer whose small business was ruined by the South Improvement Company scheme of 1871 and the conglomerate which became Standard Oil. Introduced to each other in 1902 by their mutual friend Mark Twain, Tarbell who had become an investigative journalist and Rogers, who knew of her work, shared meetings and information over a two-year period which led to her epoch work, The History of the Standard Oil Company, published in 1904, which many historians feel helped fuel public sentiment against the giant company and helped lead to the court-ordered break-up of it in 1911.

The oil heritage of Venanago County is remembered by a Pennsylvania State Park and many heritage sites which help tell the story and memorialize the people of the oil boom of the late 19th and early 20th centuries.

There were 22,747 households out of which 30.40% had children under the age of 18 living with them, 55.80% were married couples living together, 9.90% had a female householder with no husband present, and 30.00% were non-families. 26.20% of all households were made up of individuals and 12.50% had someone living alone who was 65 years of age or older. The average household size was 2.45 and the average family size was 2.93.

In the county, the population was spread out with 24.20% under the age of 18, 7.20% from 18 to 24, 26.70% from 25 to 44, 25.10% from 45 to 64, and 16.80% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 95.40 males. For every 100 females age 18 and over, there were 92.10 males.

Pennzoil and Quaker State left the Venango area for Texas. After leaving the area they merged and stopped refining oil. They now concentrate on retail oil and automotive additives produced for them by other companies. As of 2007, the two companies only exist as brand names after the company disappeared because of successive mergers.

With global crude oil prices touching US $100 in early 2008, long-dormant interest reawakened in Venango County's remaining oil reserves, 70% undrilled by one estimate. High prices make less accessible oil deposits worth extracting. For instance, a Canadian firm proposed drilling several large mines and allowing oil to flood the tunnels.[14]

Franklin Public Library. The Franklin Public Library was founded in 1894 and has had several homes, although its current location on Twelfth Street in Franklin, Venango County, PA has been its home since 1921. The original structure on Twelfth Street was built in 1849 as a residence and required extensive renovations in 1921 to make it suitable for library use.

Under Pennsylvania law, there are four types of incorporated municipalities: cities, boroughs, townships, and, in at most two cases, towns. The following cities, boroughs and townships are located in Venango County: